This invention relates to a machine for the commercial preparation of popcorn generally similar to those disclosed in U.S. Pat. Nos. 3,294,546 and 4,438,682, and particularly to a popcorn machine that is adapted to produce popcorn of the highest quality on a commercial volume basis with the least wastage.
U.S. Pat. No. 3,294,546 describes a commercial hot air popcorn machine which used a popping tube within a glass, domed popping jar for visible hot air popping of corn. Heated air was used to support a fluid bed of unpopped kernels of corn at the base of the popping tube. Popped kernels were carried by the heated air up and out of the tube and down between the tube and the jar to a collection tray beneath a lower open end of the jar. A first thermostatic switch was provided to control the feeding of unpopped corn kernels into a popping chamber at the base of the popping tube when the temperature of the chamber rose above a preset value of the switch. A feed conveyor auger was activated by the switch to feed corn into the popping chamber until the chamber temperature dropped below the cutoff value of the switch. Second and third thermostatic switches were provided to shut off three of five separate heater elements provided for air heating in the event that temperatures in the popping chamber or in the heater itself rose above predetermined values. The remaining two heater elements were manually controlled by a production switch. In this device, gross regulation of the popping chamber temperature was accomplished by the thermostatic and manual switches. Fine regulation of the popping chamber temperature was accomplished by feeding corn into the chamber to absorb heat and lower the temperature. Unfortunately, it took several consecutive initial popping cycles before equilibrium conditions and optimum operation of the machine would be reached (see Col. 13, lines 60-65). Moreover, because of the difficulty in accurately adjusting the thermostatic switch controlling the corn feed conveyor and because the popping chamber temperature was not directly controlled by continual set point adjustment of the heaters, the popping chamber temperature would tend to fluctuate over relatively broad ranges during the course of a popping cycle and result in significant wastage (percentage of unpopped kernels).
U.S. Pat. No. 4,438,682 discloses an improved commercial, glass domed popcorn popping machine including a manually-operable selector switch adapted to be set at any of four positions for selecting any of four rates of popping corn. This machine was designed for timed cyclic operation. The selector switch controlled electrical circuitry which in turn controlled the operation of a corn feed conveyor at different duty factors for feeding corn at different preselected rates. The selector switch further controlled the degree to which a damper, which regulated hot air flow through the popping chamber, opened and when it closed. The selector switch further controlled the number of individual heating elements which were energized during the cycle with an additional element being energized during each incremental advance of the switch. In addition, a trim heater was provided which was cycled on and off by a temperature controller. Thus, by mere switch change, the machine could be configured to operate at the highest popping rate during periods of peak demand and could be adjusted to operate at one of three other discrete reduced popping rates as demand required. The machine could operate at at least a minimal rate, even when demand was very low, in order to continue to attract customers and potential customers with freshly popped corn.
Machines based upon the aforesaid U.S. Pat. No. 4,438,682 included a control system with discrete, integrated circuits and a temperature controller. The latter employed an air temperature probe located in the popping chamber and included a plurality of manually adjustable potentiometers. The potentiometers could be set to output a first signal when popping chamber air temperature reached a minimum temperature at which the conveyor was enabled to feed corn, a second signal when the popping chamber air temperature reached a higher, desired popping or "cycle" temperature to cycle the trim heater and a third signal when the popping chamber air temperature reached a maximum allowable temperature to shut down the heaters and disable the conveyor. Other adjustable potentiometers were provided elsewhere in the control system to permit selection of other operating parameters such as the damper position, corn feed rates, etc. However, at least the potentiometers which were provided for adjustably setting corn feed cycle and damper settings were adjusted once during circuit assembly to preselected output levels and then potted to prevent changes in those settings. When finally installed in popping machines, these circuits were essentially hard wired and no longer adjustable. Salt and oil feed rates and popping chamber "cycle" temperature setting potentiometers were left adjustable.
In operation, it was found that the machines based on the design disclosed in U.S. Pat. No. 4,438,682 could be further improved. The discrete integrated circuit control system, the blower and the heaters employed in that machine were noticeably affected by the differences in nominal line voltage which occur from location to location around the country. It was also found that there were subtle variations in popping chambers from machine to machine which also affected the time, temperature and air flow parameters required for optimal performance. These fluctuations and variations affected the ability of the machine to operate efficiently in a predictable and repeatable manner in all environments. The actual performance of a machine at any particular location in the country could not be known until the machine was installed and operated. While the machine could be operated at four different output levels, it could not be easily adjusted or ever fully adjusted for optimal performance at any output level. Even if they could have been adjusted, there was no easy or convenient way to measure or otherwise determine important operating parameters of the machine because certain parameters varied with variations in the line voltage. Nor was there any way to predictably adjust in the field any of the parameters which could be adjusted, such as popping chamber temperature, for example. There was no easy or convenient way to measure or otherwise determine popping chamber temperature. As a result, machines built according to the aforesaid U.S. Pat. No. 4,438,682 averaged about 8% wastage in use. These inefficiencies were not known and could not be appreciated until several of the machines were built and operated under different conditions in different areas in the country.